This invention relates to the art of detecting leaks. More particularly, this invention relates to detecting volume leaks in liquid storage tanks.
Detecting small losses of liquid from a storage tank, e.g., an underground gasoline storage tank, can be very difficult. Many systems and methods have been suggested to detect such leaks. For example, Sunmark Industries, a division of Sun Oil Company of Pennsylvania, has sold a leak detecting device which relies on the principle of buoyancy, i.e., the principle that a body suspended in a liquid is buoyed up by a force equal to the weight of liquid displaced by such a body. A sensor which extends from a balance and which is partially submerged in the tank fluid detects buoyancy changes corresponding to either an increase or a decrease in the total amount of liquid in a tank.
The Kent-Moore System, see U.S. Pat. No. 3,580,055, is a method and apparatus for determining whether there are any leaks in a liquid storage container. One of the steps necessary in carrying out a determination of leaks is to fill to excess a storage zone and manually maintain a constant head on the tank. The liquid in the tank is circulated to maintain an average temperature within the tank.
There are several problems in the Kent-Moore System which result in readings which are not stable. One source of these problems involves gas bubbles which become trapped within a storage tank or zone. Since most storage tanks are not absolutely level, vapor pockets almost inevitably form as such a tank is filled to excess. Trapped gas bubbles tend to change in volume in response to changes in temperature and/or changes in pressure. Maintaining the head on the tank manually as in the Kent-Moore test can cause significant variations in pressure. During testing with the Kent-Moore System, it has been found that observed volumes often fluctuate in both a positive and negative direction. These fluctuations are believed to result from changes in sizes of trapped gas bubbles.
Another source of problems arises because the Kent-Moore System uses a pump that necessarily inputs energy into the tank. As a result of using such a pump, temperature equilibration is very difficult to achieve.
Clearly, apparatus and methods capable of easily detecting liquid leaks are both desirable and useful.